1. Field of the Invention
The present invention relates generally to image processing apparatuses, image processing methods and image processing program products, and particularly to image processing apparatuses, methods and program products capable of creating a dither matrix providing improved image quality.
2. Description of the Related Art
Conventionally in the field of laser printers and other similar image forming apparatuses it has been known that in order to display a halftone image, dithering or the like is employed to control a number of dots corresponding to a level in intensity.
Creating a dither pattern used in dithering is accompanied by such a disadvantage as follows: initially for processing an image small in resolution such as 600×1200, 1 bit, increasing the number of lines is disadvantageously accompanied by insufficient levels. For example if a pattern of 150 lines per inch (LPI) is created, only 32 levels are obtained.
There is an approach allowing γ adjustment by remaking a dither pattern. This, however, requires creating a dither pattern having a capability of reproduction of approximately 1000 levels.
An approach accommodates such issues as above by tiling a dither matrix to obtain an apparent, large number of levels.
As a technique related thereto, Japanese Laid-Open Patent Publication No. 2001-111830 discloses a method of creating a dither pattern automatically from more than 256 basic patterns.
Furthermore, Japanese Laid-Open Patent Publication No. 2002-125122 discloses a technique forming a dither pattern by putting a subsequent dot at a location remotest from a previously put dot.
Furthermore, Japanese Laid-Open Patent Publication No. 2003-87567 discloses a technique growing identically shaped dots in a dither pattern at a plurality of locations in order.
In the conventional art, however, for example some orders of tiling a dither matrix disadvantageously provide a visually unwanted texture.